The Azolla bloom in the Guadiana River (Portugal) in April 1993. Its causes
and consequences
Francisco Carrapićo1, M. Lourdes Costa2, Generosa Teixeira3, M. Helena
Costa4, António A. Frazčo5 and M. Conceićčo R. Santos4
1Departamento de Biologia Vegetal, Faculdade de Ciźncias da Universidade de
Lisboa, Bloco C2, Campo Grande, 1700 Lisboa (Centro de Biologia Ambiental -
FCUL), 2Escola Superior Agrária de Coimbra, I.P.C., Bencanta, 3000 Coimbra,
3Faculdade de Farmácia da Universidade de Lisboa, Av. das Forćas Armadas,
1600 Lisboa (Centro de Biologia Ambiental - FCUL), 4Departamento de
Ciźncias e Engenharia do Ambiente, Faculdade de Ciźncias e Tecnologia da
Universidade Nova de Lisboa, Quinta da Torre, 2825 Monte de Caparica and
5Direcćčo Regional do Ambiente e Recursos Naturais do Alentejo, Rua 24 de
Julho, 1, 2ľ E, 7000 Évora.
Azolla is a free-floating aquatic fern that in some environmental
conditions can become a weed. In Portugal the genus Azolla is represented
by two species (Azolla filiculoides and Azolla caroliniana) which grow in
several hydrographic basins. In this communication, we analyze an Azolla
bloom in the Guadiana river (South of Portugal) in what concerns its
characteristics and causes in a global perspective of the ecological and
social impacts of this situation, associated with the difficulty of the
authorities to deal with this unusual problem, that became a national
event.
In the last four years the climatic condition in Portugal, namely in the
South, was characterized by the lower pluviometry with long dry seasons.
These environmental characteristics associated with the presence of several
river dams, have led to the appearing of lower flows during the year (≤1
m3.s-1 in several points of the river). By the other hand, agricultural
activity developed in the upper area of the Guadiana hydrographic basin
(the global basin area has about 67000Km2), associated with the presence of
several industries and specially with the untreated domestic effluents from
several towns and villages in Spain and Portugal, have contributed to the
organic contamination actually shown by the Guadiana river. The phosphate
contents have increased, during the firsts months of 1993 in different
river sites, with a maximum concentration values in April, between 12.3 and
1.46 mg l -1 P2O5, which are considered one of the main causes of the
Azolla bloom.
Azolla exists normally in small channels near by or in restricted zones of
the upper Guadiana river where the species referred is Azolla caroliniana,
but in the present case (lower Guadiana river) the fern bloom species is
composed by Azolla filiculoides. The number of sporulated plants in 1993
was higher (≥ 75%), which probably have happened in the last three years,
during similar stressed climatic conditions. This fact, associated with the
nutrients concentration in the river, namely the P2O5 and NH4, allowed the
fern to make a progressive occupation of new ecological spaces, ending with
the bloom observed in 1993, extended for several kilometers in the
Portuguese sector of the Guadiana river. All these facts suggest a
reflection on the issue and to share the experience with others colleagues
and environmental authorities. At last, a management model for the use of
the large fern biomass produced is suggested, using some of its
physiological and biochemical characteristics.
For further informations please contact: Francisco Carrapićo - FCUL/DBV -
Lisbon, Portugal (F.Carrapico@cc.fc.ul.pt).
Thank you,
Francisco
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Subject: Azolla spp.
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Date: Thu, 29 Apr 1993 15:20:37 -0500 (CDT)
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I am looking for practical information on Azolla research of
use by farmers in the United States for a green manure in
rice production.